Uplink control information may include scheduling request, acknowledgement (positive acknowledgement/non-acknowledgement (ACK/NACK)) information for downlink transmission, downlink channel status information, etc. In this case, the ACK/NACK information for downlink transmission is the control information fed back from a downlink receiving entity to a downlink transmitting entity depending on success of decoding of downlink data. In more detail, if the downlink receiving entity successfully performs decoding of downlink data, it may feed ACK information back to the downlink transmitting entity. If not so, the downlink receiving entity may feed NACK information back to the downlink transmitting entity.
Meanwhile, the introduction of a multiple carrier technique has been considered to support the more extended bandwidth than the related art bandwidth. The multiple carrier technique may be referred to as the carrier aggregation technique. In a general wireless communication system according to the related art, one carrier is only used on an uplink and a downlink, whereas the multiple carrier technique is intended that a plurality of carriers are grouped physically in a frequency domain to support an extended bandwidth, whereby a frequency bandwidth of a logically great band may be used. If the multiple carrier technique is applied to downlink transmission, a plurality of downlink data may be transmitted through a plurality of downlink data channels on a plurality of downlink carriers (or downlink cell (DL cell)) at a specific time. Accordingly, the downlink receiving entity may be required to feed a plurality of kinds of ACK/NACK information on a plurality of downlink data back to the downlink transmitting entity.
Alternatively, a time division duplex (TDD) system in which downlink transmission and reception and uplink transmission and reception are performed at respective time periods (for example, subframe), it may be required that a plurality of kinds of ACK/NACK information on a plurality of downlink data transmitted from a plurality of downlink subframes should be fed back.